Flash-type distillation system



Oct. 13, 1959 H. E. BETHON 2,908,618

FLASH-TYPE DISTILLATION SYSTEM Filed June 5, 1957 n: m 0 m z m Q E 2 S m a o l- 2 E a 3 INVENTOR HENRY E. BETHON In O ATTORNEYS United States Patent 1 2,908,618 FLASH-TYPE DISTILLATION SYS'IEM Henry Edwin Bethon, Washington, D.C., assignor to the United States of America as represented by the Secretary of the Navy Application June 5, 1957, Serial No. 666,264 3 Claims. (Cl. 202-174) This application is a continuation-impart of applicants copending application Serial No. 365,301, filed June 30, 1953, for Flash-Type Distillation System.

The present invention relates to a system for distilling water and more particularly to a distilling system capable of quiet operation. More particularly, this invention relates to a sea water distilling system for use on submarines.

The operation of submarines in modern warfare requires an extremely low level of radiated noise in order to prevent detection of the vessel by hostile units in the area. However, large quantities of pure water are also required for use in batteries and for use by the crew, and

it is impractical to use very high power for short periods of time to distill the required quantity of water for storage because of the space and power restrictions of the vessel. It therefore becomes necessary to provide distillation equipment which requires moderate power and produces a minimum noise so that it may be operated over extended periods of time.

The distillation equipment used at present has proved unsatisfactory, because it requires frequent cleanings (chemical), has inadequate capacity after extended periods of operation, and produces excessive noise. Many of these problems are caused or accentuated by the evaporation of contaminated water at pressures above atmospheric by contact with a heated surface which deposits the contaminationon the heated surface in the form of a scale. In general, the scale is an insulator which reduces the efficiencyof the unit, and must be removed periodically either by dismantling the equipment for mechanical cleaning or by resortingto chemical cleaning. The vapor compression distillation unit has been widely used but suffers from the defects that it scales rapidly, is hard to clean, and requires a large motor driven compressorwhich generates a high noise level.

It is an object of the present invention to provide a distillation system which is simple to operate and maintam.

It is another object of the present invention to provide a distillation system which requires only a moderate amount of'power. a

It is a further object of the present invention to provide a distillation system which is capable of continuous operation for extended periods of time.

It is a still further object of the present invention to provide a distillation system producing a minimum amount of noise. i

It is afurther object of the present invention to proivide a distillation system wherein water is not evaporated in contact with externally heated surfaces. 1 7 Other objects and the many attendant advantages of the present invention will be made apparent to. those skilled in the art by reference to the following detailed description and to the "appended drawing in whichthe single figureillust'rates in schematic form, a distillation system made'in accordance with the present invention.

It is .believedvthat'a brief summary of the invention 1 is helpfulviri understanding the operation and the detailed description. [Referring to the drawings, contaminated water, such as seawater, is introduced into the distillabecome encrusted with scale.

tion system by a feed pump 11 which forces this water through a pair or heat exchangers 14 and 13. The feed water is fln'ther heated in passingthrough a series of heat exchangers 15 positioned at the upperends of respective evaporator units 17, and is still further heated to a temperature near its boiling point in a water heater 19. The heated feed water then passes into the first of a series of serially connected lower compartments of evaporator units 17.

The evaporator'units 17 are sealed vessels, connected to a vacuum pump 21 which produces pressures therein below atmospheric pressure, the pump 21 being required to remove only the noncondensable gases and vapors in the system, so that it may be small. The pressures in the respective evaporator units are arranged in decreasing order, and water which does not evaporate in one evaporator unit may evaporate in a latter unit. As the water is evaporated, it leaves its contaminating materials in the remaining'water, so that the contaminated water containing a concentration of contaminating materials is removed from the last evaporator unit 17 by a discharge pump 23 through the heat exchanger. 14.

The vapor or steam produced in each of the several evaporator units 17 passes upward past a baflle 25, where it comes in contact with the heat exchanger 15 which is at a considerably lower temperature and therefore condenses the vapor to distillate. The distillate is conducted by a distillate line 27 through the heat exchanger 13 where it is cooled by heating the incoming feed water. A distillate pump 29 is used to remove the distillate from the system for storage.

It will be noted that the feed Water is not evaporated by means of contact with heated surfaces which rapidly Thefeed water is evaporated by its own internal heat, so that upon evaporation, the impurities are merely left in the remaining water to be removed from the last evaporation unit by the discharge pump 23.

The feed pump 11 may be of any desired type, and is connected to a' source of water to be distilled by means of a tube 31, the discharge side of the pump being conneeted by a tube 33 to the heat exchanger 13. The heat exchanger 13 may be of any desired type, and is illustrated as having a single tube only to simplify the explanation thereof. The incoming feed water may have a temperature of 70 F. and be heated to about F. in passing through the heat exchanger 14, and to about 117 F. in passing through the heat exchanger 13, while the distillate from the distillate line 27 is cooled from about F. to about 85 F.

The evaporator units 17A, 17B, 17C, 17D, 17E, and 17F are of similar construction, and each comprises an upright sealed vessel which is divided into two compartments by the baifie 25, the lower compartment containing water to be evaporated in succeeding stages and the upper compartment containing a heat exchanger 15 which is in intimate contact with any steam moving from the lower compartment to the upper compartment and which provides a'water path therethrough for feed water. An inlet 35 and an outlet 37 are provided in the lower compartment, while a vent 39 equipped with a valve 41 and a distillate connection 43 are provided in the upper compartment. A U-tube 36, containing a pressure-balancing liquid column of feed water, connects the outlet 37 of one evaporator unit to the inlet 35 of the next adjacent unit.

15 and vapor yvhereby toinsure condensation of the distillate. The baffle 25 facilitates the separation of entrained contamination fromjfthe'vapor'and also serves to conduct the distillate to the distillate connection 43.

The vent connections 39 are connected through the valves 41 to a vacuum line 42 and thereby to the vacuum pump '21, so that the valves 41 may be used to adjust the pressures within the respective evaporator units 17. As shown in the drawing and as pointed out hereinafter, the pressures are successively decreased in the several evapo rator units in the direction of flow of feed water therethrough. v

The heat exchanger units 15 are serially connected, and receive feed water from the heat exchanger 13. The feed water is heated in passing through the several units, and the outlet of the last of the heat exchangers 15 is connected to the inlet of the Water heater 19.

In a broad concept of the invention, the water heater 19 may be of any desired type, since the water is not evaporated therein. However, in the specific embodiment of the invention it is desirable to dispense with open flames and other direct heaters and to reduce scaling to a minimum, and for this reason, the water heater 19 is illustrated as employing distilled water to transfer heat from electric heating elements to the feed water.

The lower compartments of the several evaporation chambers 17 are also serially connected, the outlet 37 of the unit 17F being connected by a pressure-balancing U- tube 36 to the inlet 35 of the unit 17E, andso on. The inlet 35 of the evaporation unit 17F is connectedto receive heated feed water from the water heater 19 and the outlet 37 of the unit 17A is connected to the discharge pump 23.

In accordance with this invention, the water heater 19 comprises a closed vessel 49 having a plurality of heat exchanger tubes 51 at the upper end and one or more electric heating elements 53 at the lower end. Distilled water, indicated at 55, is placed in the vessel 49, and the operation of the electric heating elements is controlled by means of a thermostat 57 to maintain a desired feed water temperature. In operation, the distilled water 55 is evaporated by the electric heating elements 53, and the steam thus produced is condensed by the feed water in the heat exchanger tubes 51 to heat the feed water to a ternperature below its boiling point. A gauge glass54, which may take the form of a water column is provided on the vessel 49 to indicate the level of the distilled water therein.

A back pressure valve 56 is provided in the outlet of the water heater 19 to maintain the inlet portion of the distillation system at a pressure which will prevent evaporation of the water therein before reaching the evaporation chambers 17. Thus, by utilizing the back pressure valve and by employing distilled water, a constant boiling point secondary heat transfer medium, it is assured that there will be no boiling of feed water in the heat exchanger tubes 51. The heated contaminated water is caused to flow through the back pressure valve 56 into the evaporator units 17, one after another, wherein a large part of the water is evaporated as it is subjected to the series of decreasing pressures.

Since the introduction of steam into a hydraulic pumping system will interfere with proper pumping, the condensate line 27 is connected through a flash chamber 59, which produces a water seal to prevent steam from reaching the pump. A gage glass 61 is provided on the flash chamber to indicate the water level therein. As an example of pressures and temperatures suitable for use in the several evaporator units, the following values have been found practical:

There is, of course, heat remaining in the brine leaving the evaporation unit 17A, and a part of this heat is recovered in the heat exchanger 14 which is inserted in the feed water line 33.

It is desirable that all exterior surfaces of the heat exchangers, evaporator units, water heater and piping be insulated in order to minimize heat losses in the system and to thus reduce the quantity of electricity required by the water heater 19. The pumps 11, 21, 23, and 29 may be driven by separate motors or may be combined for operation from two or more motors. For instance, pumps 11 and 23 may be driven from a single motor while pumps 21 and 29 are driven from another.

The distillation system is preferably composed of several assemblies to facilitate installation and maintenance. However, it will be apparent to those skilled in the art that the several components may be mounted as a single package unit if desired. The pumps and the driving motors may be mounted on vibration-isolation mountings and are preferably enclosed in compartments containing sound insulation.

In order to place the system in operation, the vacuum pump 21 and the electric heating elements 53 are started. When the distilled water 55 is boiling and the vacuum in the evaporator units 17 reaches the proper operatingpressure, the feed pump 11 and the discharge pump 23 are started, and the system soon reaches its normal operating temperatures.

When it is desired to take the system out of operation, the electric heating elements 53 are cut off, and when no more distillate forms, pumps 21 and 29 may be stopped. The pumps 11 and 23 are preferably left running for a few minutes to clean the system of brine, scum, etc.

While only a preferred embodiment of the present invention has been described, it will be apparent that many changes and modifications of the system may be made without departing from the spirit thereof and it is intended to cover all such embodiments as fall within the scope of the appended claims.

What is claimed is: n

1. In a sea water distillation system, a plurality of closed evaporation units each having a lower evaporating chamber, an upper condensing chamber in vertical alignment with the lower chamber and a baflle therebetween, the lower evaporating chamber and upper condensing chamber of each of said units being otherwise in open and unobstructed communication one with the other for flow of vapor from the former to the latter, each of said evaporating chambers having inlet and outlet connections for flow of feed water therethrough with the outlet connection of one evaporating chamber forming the inlet connection to the next evaporating chamber for series flow of feed water through the plurality of evaporating chambers from the first to the last of such chambers in a predetermined direction of flow, said inlet and outlet connections each comprising a pressure-balancing U-tube having a down leg and an up leg with the up leg arranged to discharge feed water at a higher elevation than the level of feed water in the down leg thereby forming pressure-balancing liquid columns between adjacent evaporating chambers, said evaporating chambers being otherwise in unobstructed and open communication one with the others for series flow of feed water therethrough, a heat exchanger in each of the condensing chambers, each of said heat exchangers having an inlet and an outlet connection for flow of feed water therethrough with the outlet connection of one heat exchanger forming the inlet-connection of the next heat exchanger for series flow of feed water therethrough, which feed water flows through the heat exchangers in opposite direction to the predetermined direction of flow of the feed water'- through the evaporating chambers,means for supplying feed water "to be=distilled to the first of the heat exchangers, means connecting the last of the heat exchangers to thefirst of the evaporating chambers in their respective directions of how for flow of feed water from the former to the latter, indirect heating means in said last-named connection 'for heating the feed water to a temperature near its boiling point prior to flow thereof into the first of the evaporating chambers, means connected to an upper portion of each of the condensing chambers, for reducing the pressure in each of the evaporating units below the vapor pressure of feed water therein at the existing temperature thereof whereby at least a portion of the feed water is vaporized by its O'WH internal heat in each of the evapoarting chambers and the resultant water vapor is condensed by the heat exchanger in the respective condensing chamber, said pressure reducing means including a vacuum pump, a manifold connected to the inlet side of the vacuum pump, conduits connecting the upper portion of each of the condensing chambers to the manifold in a manner as to exhaust noncondensable gases therefrom while reducing the vapor pressure therein, a pressure regu- 'lating valve in each of said conduits, said pressure regulating valves being adjusted in a manner such that the 20 pressures in the respective evaporation units are arranged in decreasing order in the direction of flow of feed water therethrough, means for removing condensate from each of the condensing chambers, and means for removing the residue feed water from the last of the evaporating chambers.

2. A distillation system as set forth in claim 1 wherein the indirect heating means includes a closed evaporation-condensation unit containing a secondary heat ex- 6 I change medium, means for vaporizing the secondary heat exchange medium in said closed unit, and means for condensing the resultant vapor, said last-named means including a heat exchanger having an internal passage for flow of feed Water therethrough and an external surface for contact with said resultant vapor.

3. A distillation system as set forth in claim 1 wherein the means for removing condensate from each of the condensing chambers includes the baflies between each of the evaporating and condensing chambers, a condensate manifold and a conduit between each of the baflles and the condensate manifold for parallel flow of condensate from each of the condensate chambers to the condensate manifold.

References Cited in the file of this patent UNITED STATES PATENTS 450,361 Baird April 1891 643,702 Waterhouse Feb. 20, 1900 2,165,044 Fox et al. July 4, 1939 2,280,093 Kleinshmidt Apr. 12, 1942 2,389,064 Latham Nov. 13, 1945 2,389,789 Latham Nov. 27, "1945 2,475,482 Clements July 5, 1949 2,759,482 Worthen et a1. July 5, 1949 OTHER REFERENCES Depantment of Interior, Demineralization of Saline Water with Solar Energy, 1954, page 23 and Figure 5. 

1. IN A SEA WATER DISTILLATION SYSTEM A PLURALITY OF CLOSED EVAPORATION UNITS EACH HAVING A LOWER EVAPORATING CHAMBER, AN UPPER CONDENSING CHAMBER IN VERTICAL ALIGNMENT WITH THE LOWER CHAMBER AND A BAFFLE THEREBETWEEN, THE LOWER EVAPORATING CHAMBER AND UPPER CONDENSING CHAMBER OF EACH OF SAID UNITS BEING OTHERWISE IN OPEN AND UNOBSTRUCTED COMMUNICATION ONE WITH THE OTHER FOR FLOW OF VAPOR FROM THE FORMER TO THE LATTER, EACH OF SAID EVAPORATING CHAMBERS HAVING INLET AND OUTLET CONNECTIONS FOR FLOW OF FEED WATER THERETHROUGH WITH THE OUTLET CONNECTION OF ONE EVAPORATING FORMING THE INLET CONNECTION TO THE NEXT EVAPORATING CHAMBER FORMING THE SERIES FLOW OF FEED WATER THROUGH THE PLURALITY OF EVAPORATING CHAMBERS FROM THE FIRST TO THE LAST OF SUCH CHAMBERS IN A PREDETERMINED DIRECTION OF FLOW, SAID INLET AND OUTLET CONNECTIONS EACH COMPRISING A PRESSURE-BALANCING U-TUBE HAVING A DOWN LEG AND AN UP LEG WITH THE UP LEG ARRANGED TO DISCHARGE FEED WATER AT A HIGHER ELEVATION THAN THE LEVEL OF FEED WATER IN THE DOWN LEG THEREBY FORMING PRESSURE-BALANCING LIQUID COLUMNS BETWEEN ADJACENT EVAPORATING CHAMBERS, SAID EVAPORATING CHAMBERS BEING OTHERWISE IN UNOBSTRUCTED AND OPEN COMMUNICATION ONE WITH THE OTHERS FOR SERIES FLOW OF FEED WATER THERETHROUGH, A HEAT EXCHANGER IN EACH OF THE CONDENSING CHAMBERS, EACH OF SAID HEAT EXCHANGERS HAVING AN INLET AND AN OUTLET CONNECTION OF ONE HEAT EXCHANGER FORMING THE THE OUTLET CONNECTION OF ONE HEAT EXCHANGER FORMING THE INLET CONNECTION OF THE NEXT HEAT EXCHANGER FORMING THE FLOW OF FEED WATER THERETHROUGH, WHICH FEED WATER FLOWS THROUGH THE HEAT EXCHANGERS IN OPPOSITE DIRECTION TO THE PREDETERMINED DIRECTION OF FLOW OF THE FEED WATER THROUGH THE EVAPORATING CHAMBERS, MEANS FOR SUPPLYING FEED WATER TO BE DISTILLED TO THE FIRST OF THE HEAT EXCHANGERS, MEANS CONNECTING THE LAST OF THE HEAT EXCHANGERS TO THE FIRST OF THE EVAPORATING CHAMBERS IN THEIR RESPECTIVE DIRECTIONS OF FLOW FOR FLOW OF FEED WATER FROM THE FORMER TO THE LATTER, INDIRECT HEATING MEANS IN SAID LAST-NAMED CONNECTION FOR HEATING THE FEED WATER TO A TEMPERATURE NEAR ITS BOILING POINT PRIOR TO FLOW THEREOF INTO THE FIRST OF THE EVAPORATING CHAMBERS, MEANS CONNECTED TO AN UPPER PORTION OF EACH OF THE CONDENSING CHAMBERS, FOR REDUCING THE PRESSURE IN EACH OF THE EVAPORATING UNITS BELOW THE VAPOR PRESSURE OF FEED WATER THEREIN AT THE EXISTING TEMPERATURE THEREOF WHEREBY AT LEAST A PORTION OF THE FEED WATER IS VAPORIZED BY ITS OWN INTERNAL HEAT IN EACH OF THE EVAPORATING CHAMBERS AND THE RESULTANT WATER VAPOR IS CONDENSED BY THE HEAT EXCHANGER IN THE RESPECTIVE CONDENSING CHAMBER, SAID PRESSURE REDUCING MEANS INCLUDING A VACUUM PUMP, A MANIFOLD CONNECTED TO THE INLET SIDE OF THE VACUUM PUMP, CONDUITS CONNECTING THE UPPER PORTION OF EACH OF THE CONDENSING CHAMBERS TO THE MANIFOLD IN A MANNER AS TO EXHAUST NONCONDENSABLE GASES THEREFROM WHILE REDUCING THE VAPOR PRESSURE THEREIN, A PRESSURE REGULATING VALVE IN EACH OF SAID CONDUITS, SAID PRESSURE REGULATING VALVES BEING ADJUSTED IN A MANNER SUCH THAT THE PRESSURES IN THE RESPECTIVE EVAPORATION UNITS ARE ARRANGED IN DECREASING ORDER IN THE DIRECTION OF FLOW OF FEED WATER THERETHROUGH, MEANS FOR REMOVING CONDENSATE FROM EACH OF THE CONDENSING CHAMBERS, AND MEANS FOR REMOVING THE RESIDUE FEED WATER FROM THE LAST OF THE EVAPORATING CHAMBERS. 